Hyundai code P0128? (TOP 5 Tips)

The most common cause for P0128 in a Hyundai is the engine coolant thermostat is stuck open. When the thermostat does open, hot coolant should start to flow and quickly warm up the radiator hose. If the radiator hose heats up slowly, the thermostat is stuck open or opening prematurely and needs to be replaced.

Is it safe to drive with P0128 code?

Can I drive my vehicle with a P0128 trouble code and illuminated CEL? You may drive your vehicle with a P0128 trouble code. You will not notice any issue except for maybe the temperature gauge never reaching normal levels, and possibly the Check Engine light being illuminated.

How serious is P0128 code?

The P0128 code is set when the engine control module (ECM) determines that coolant temperature is lower than the original equipment thermostat’s opening temperature. To put it another way, the engine is running too cool or the temperature does not increase quickly enough.

What happens if you drive with a bad coolant temperature sensor?

The engine will run rich, so you’ll smell raw gas, and you may see black smoke from the tailpipe. Unplugging the engine coolant temperature sensor before starting the engine may result in a no-start, especially likely on a cold morning.

Can low coolant cause P0128?

Low engine coolant can alter the engine running temperature enough to signal trouble code P0128. Your intake air temperature sensor, coolant temperature sensor and coolant fan could also signal this trouble code, so these should be inspected after you look over your thermostat and coolant level.

What causes P0128 code?

The most common cause for P0128 is the engine coolant thermostat is stuck open. When the thermostat does open, the hot coolant should start to flow and quickly warm up the radiator hose. If the radiator hose heats up slowly, the thermostat is stuck open or opening prematurely and needs to be replaced.

How do I know if my coolant temp sensor is bad?

Bad Coolant Temperature Sensor Symptoms

  1. Check Engine Light.
  2. Poor Mileage.
  3. Electrical Cooling Fans not coming on.
  4. Black Smoke from the Exhaust Pipe.
  5. Difficult Starting Condition.
  6. Engine Overheats.
  7. Poor Idling.
  8. Poor Engine performance.

Will a bad thermostat throw a code?

the most noticeable issues occur when the thermostat gets stuck in either the open or closed position. a malfunction can result in a trouble code, generated by the engine’s computer, which can turn on your check engine light.

Where is coolant temperature sensor?

On most vehicles, the coolant temperature sensor (CTS) can be found somewhere near the engine thermostat, which allows it to function optimally. The tip of the CTS is probably located right next to the engine coolant.

Can low coolant cause a misfire?

Internal coolant leaks can foul a spark plug and cause a misfire. Unfortunately, it also means that drivers will run a vehicle with a coolant leak for several thousand miles while the plug becomes slowly fouled.

Where is the engine thermostat located?

Most cars have a top-mounted thermostat located close to the water pump on the cylinder head. The top radiator hose feeds coolant through the thermostat into the engine. If you can’t locate the thermostat, simply follow the hose until you see the housing containing the thermostat where the hose joins the engine.

How do you fix low coolant temp?

The easiest way how to fix low coolant is to begin filling your coolant back to acceptable levels and allow the coolant to soak back into the system. Upon opening your radiator cap, you will see indicators such as “max” and “min” which indicates the level of the coolant mixture currently in your tank.

Can a coolant temp sensor keep a car from starting?

The sensor will not cause a no start. It could cause a hard start and a rich or lean condition only.

What are the signs of a bad thermostat?

5 Symptoms of a Bad Thermostat (and Replacement Cost)

  • #1 – Temperature Gauge Reading Higher (or Lower) Than Normal.
  • #2 – Sudden Air Temperature Changes Inside Vehicle.
  • #3 – Coolant Leaking.
  • #4 – Rumbling Noises.
  • #5 – Heater Malfunction.

Why is my car reading hot but not overheating?

If you find that you’ve got a car running hot but not overheating there might be a few reasons: Clogged or damaged radiator. Low coolant level. Damaged water pump or thermostat.

Hyundai Elantra P0128: Coolant Thermostat – Below Temp

It is a rather common OBDII issue code, with the code P0128 being the most prevalent. It is activated if the coolant temperature in your Hyundai Elantra does not reach the correct operating temperature within a specified time period. It is a generic powertrain code, which implies that it will have the same meaning regardless of who made the car (1996 and after).

Elantra P0128 Symptoms

Unless it becomes chilly, there aren’t many symptoms associated with P0128. The following are the symptoms that are related with this error code:

  • When the Hyundai Elantra receives the P0128 fault code, the most noticeable symptom is likely to be a lack of heat. When the thermostat fails to get the engine up to the right operating temperature completely, it indicates that the water passing through the heater core is not as hot as it should be. As a result, there is reduced or no heat. With the exception of the heater not functioning properly, the only additional symptom associated with P0128 is often the presence of the service engine soon light itself

P0128 Causes: Hyundai Elantra

Due to the fact that the thermostat is responsible for 90 percent of all P0128 errors, repairing the code is typically a straightforward process. The following are the most often seen causes of P0128:

  • Generally speaking, the most common reason of the P0128 error code is going to be a thermostat that has been left open for an extended period of time. When a thermostat is jammed open, coolant is allowed to run through the engine at all times, which is dangerous. When this occurs, the engine is ‘over-cooled,’ which means that it never achieves the correct operating temperature. How to Replace a Thermostat (with Pictures) (video). Temperature regulator Elantra
  • A issue with the wiring/sensor related with engine water temperature sensing or with the coolant temperature sensor itself may occur if the thermostat is not malfunctioning.
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Hyundai Elantra P0128 Diagnosis

Generally speaking, the most common reason of the P0128 error code is going to be a thermostat that has been left open for an extended amount of time. It is possible to have a thermostat that is permanently open, which permits coolant to flow through the engine at all times. As a result, the engine is ‘over-cooled,’ and it never achieves the appropriate operating temperature. Changing a Thermostat: A Guide (video). Temperature control with the Elantra A issue with the wiring/sensor related with engine water temperature sensing or with the coolant temperature sensor itself may occur if the thermostat isn’t the source of the problem.


In the short term, P0128 does not pose a major threat to the driveability of your Elantra. It should be mentioned that most contemporary fuel-injected engines prefer to operate at temperatures of 200 degrees or higher. Allowing them to run at too low a temperature for a lengthy period of time might cause difficulties. Have a great time figuring out what is wrong with your Elantra!

Hyundai code P0128

Hyundai has published a service bulletin11-FL-003 to remedy a Hyundai code P0128 that has been identified in the cars detailed below. The Hyundai code P01282011MY SONATA 2.4L2010MY SANTA FE 2.4L is for a 2011 Hyundai Sonata 2.4L. The service bulletin is applicable to cars equipped with the 2.4L engine that store a P0128 coolant thermostat code when the heater/defroster is used at maximum blower speed and high heat setting, as shown in the table below. To resolve the issue, replace the thermostat, cooling intake, and gasket with new or updated parts as needed.

  • 2.
  • 3.
  • 4.
  • Tensile strength: 7.8 to 11.8NM (0.8 to 1.2kgfm, 5.8 to 8.7lb-ft) Tightening torque NOTE: The new thermostat is equipped with a jiggle pin that allows air to be bled from the cylinder head.

5. Drain, clean, and re-fill the engine’s coolant reservoir. In 2015, Rick Muscoplat developed the 25630-2G710 FITTING-COOLANT INLET25500-23010 THERMOSTAT ASSY25633-2G000 GASKET-WITH-INLET FITTING. Rick Muscoplat posted a blog entry on


Hyundai P0128 Engine Coolant Temperature Below Thermostat Regulating Temperature – Car OBD Codes

This signifies that the engine’s PCM has recognized that the engine has not achieved the appropriate temperature level within a set period of time after starting the engine. The P0128 Hyundai code is intended to identify a defective thermostat in a Hyundai vehicle. P0125 Hyundai is a code that is similar. When determining whether or not the engine has reached a ‘normal’ temperature, the length of time the vehicle has been running, the readings from the intake air temperature (IAT) sensor, the reading from the engine coolant temperature (ECT) sensor, and the speed of the vehicle are all taken into consideration.


Hyundai P0128 OBD code symptoms that may occur include With the exception of the MIL lighting, you will most likely not notice any drivability issues.


HyundaiA code P0128 may be caused by a number of different factors. Hyundai might indicate that one or more of the following events have occurred: Engine coolant is at a low level. Thermostat that leaks or is jammed open The cooling fan is not working properly (running too much) Sensor for coolant temperature (ECT) that is not working properly The intake air temperature (IAT) sensor is faulty.

Possible Solutions

Based on previous experience, it appears that replacing the thermostat is the most likely option. However, the following are some recommendations for troubleshooting and resolving a P0128 Hyundai OBD-II code: Check the coolant’s strength level. Check to see that the cooling fan is operating properly (and that it is not running more than it should). If required, replace the item. Check that the engine coolant temperature (ECT) sensor is functioning properly, and replace it if required. Check that the intake air temperature (IAT) sensor is functioning properly, and replace it if required.

For a Nissan car, look for Technical Service Bulletins (TSBs), since the ECM may need to be reprogrammed to fix the P0128 Hyundai code.

The OBD2 Code Information Be Applicable For Hyundai:

Hyundai i30, Hyundai i20, 2013 Hyundai Sonata Hyundai Santa Fe, model year 2013. Hyundai Langdong, model year 2013. Hyundai HB20X, Hyundai HB20S, 2013 Hyundai HB20X, 2013 Hyundai HB20S, Hyundai HB20, model year 2013. Hyundai i40, model year 2012. 2011, 2012, 2013 Hyundai ix35, 2012, Hyundai ix20, 2011 Hyundai i10, 2011 Hyundai Verna, 2011 Hyundai Santa Fe, 2011 Hyundai Tucson, 2011 Hyundai Santa Fe Sport. Hyundai Sonata, Hyundai Azera, 2011 Hyundai Sonata, 2011 Hyundai Azera, Hyundai Avante, model year 2011.

  1. Hyundai ix55, model year 2009.
  2. Hyundai Sonata, model year 2009.
  3. Hyundai i30, model year 2008.
  4. Hyundai Veracruz, model year 2007.

(2007) Hyundai Coupe, (2006) Hyundai Getz, (2007) Hyundai Sonata, (2007) Hyundai Veloster, (2007) Hyundai Sonata Sport, (2007) Hyundai Veloster, (2007) Hyundai Sonata Sport, (2007) Hyundai Sonata Sport, (2007) Hyundai Sonata Sport, (2007) Hyundai Getz, (2007) Hyundai Sonata Sport, Hyundai Tucson, model year 2005 Hyundai Trajet, Hyundai Terracan, 2005 Hyundai Trajet, 2005 Hyundai Terracan, Hyundai Sonata, model year 2005 Hyundai Santa Fe, model year 2005 Hyundai Portico Concept from 2005.

Hyundai Matrix, model year 2005 Hyundai HED 1 Concept from 2005.

Among the Hyundai models available are the Atos Prime (2004 model), Accent (2004 model), CCS Concept (2003 model), and Sonata (2004 model). Hyundai HCD 7 Concept (2002 model year), Hyundai HCD 6 Concept (2001 model year).


1. The list of vehicle manufacturers on the right-hand side of the display screen. The Hyundai brands are represented by the ODB-ii codes that are currently in use. 2. Use the search box to look for any other OBD II Trouble Codes that may exist. In the search box, type in the five-character problem codes and hit the ‘Search’ button. Remember that a particularOBD-II code does not always represent the same thing across different vehicle manufacturers, since there are numerous different manufactures specific codes in use.

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This is because not allOBD2 codes used by one manufacturer are also used by other manufacturers.

The material included on this website is provided solely for the purpose of providing general information.

If you have any questions or concerns about the repairs on your car, please speak with your mechanic.

Hyundai GENESIS(BH) 2012 Fault Code: p0128

Follow @AutoHexII on Twitter. Description in broad terms An automated thermostat, located between the engine and the radiator, regulates the quantity of water flowing through it so that the engine coolant temperature is maintained at a predetermined level by the engine control module (ECM). When the engine coolant temperature hits around 80 degrees Celsius (176 degrees Fahrenheit), the wax in the thermostat is exhausted in order to open the valve. In the other case, if the coolant temperature is low, the wax in the thermostat contracts, causing the valve to be shut off.

DTC (Description of the DTC) P0128 is set when the coolant temperature does not reach the target temperature by the time the test timer reaches the threshold time under detecting conditions.

  • Aspects of this item include: Detecting Condition, Possible Cause, DTC Strategy, Thermostat open stuck monitor, Thermostat stuck, Enable Conditions, and more. Temperature: -7.0?(19.4?)IAT temp57?(134.6?)
  • -7.0?(19.4?)ECT temp57?(134.6? )
  • IAT at the start: -5.0?(41?)
  • IAT at the end: -5.0?(41?) Threshold value
  • Low speed drive (25mph) to driving time ratio of 0.7
  • When the test timer reaches the threshold time, the coolant temperature does not reach the target temperature. Diagnosis Time
  • s-
  • s MIL On Condition
  • s2 Driving Cycles

Code P0128 – Coolant Temperature Below Thermostat Regulating Temperature

Date last updated: July 31, 2021 The codeP0128 – Coolant Temperature Below Thermostat Regulating Temperatureindicates that the engine has not reached the anticipated temperature after being operated for an appropriate amount of time, or, in other words, that it is taking an excessive amount of time to warm up. In frigid conditions, this code frequently causes the Check Engine light to illuminate and then turn off.


There might be no symptoms at all, or there could be any of the following symptoms associated with the code P0128: Because of the cold weather, the engine takes a long time to warm up; the engine temperature lowers when driving on the highway, especially in the winter; the air conditioner and (or) temperature gauge quit working; and (or) the Check Engine light illuminates (GM).

Is it safe to drive with the code P0128?

If the car is in good running condition, the coolant level is enough, there is sufficient heat, and there are no other driving difficulties, it is conceivable that the thermostat is stuck intermittently.

In general, this is not a major issue, however it may have an impact on the gas mileage in some cases. We would nevertheless recommend that you get the car inspected by a mechanic.


Low amount of coolant Sensor for measuring the temperature of the coolant The following are examples of common causes: Incorrect or stickythermostat – The thermostat seal is not sealing properly, allowing coolant to bypass a closed thermostat – Faulty engine coolant temperature (ECT) sensor – Engine computer (PCM) software needs to be updated – Low coolant level – Radiator fan does not turn off – Faulty intake air temperature (IAT) sensor

How the code P0128 is diagnosed:

The Torque app is being used to check the engine temperature. First and first, a simple check beneath the hood must be carried out: is the coolant level satisfactory? Check to see that the engine coolant temperature sensor connector is free of corrosion and that it is correctly connected. Do you know whether there are any service bulletins? The following step is to check to determine if the engine temperature sensor is functioning properly. You should check the engine temperature when the engine is cold if you have a scan tool that can record live data.

  1. Drive the car for 10 minutes and then check the engine temperature again; it should be between 180 and 220 degrees Fahrenheit (82 and 105 degrees Celsius).
  2. An ohmmeter can be used to test the engine temperature sensor if you don’t have access to a scan tool.
  3. More information may be found at: Symptoms, issues, and testing for the engine coolant temperature sensor are all covered in this article.
  4. It is common practice to replace a thermostat anytime the code P0128 is present.
  5. This may be done at your local dealer and costs between $80 and $120 if the vehicle is not still under warranty.

Common problems causing the code P0128 in different cars:

The code P0128 is frequently associated with a faulty thermostat in numerous General Motors vehicles (including the Chevrolet Trailblazer, Chevrolet Silverado, Chevrolet HHR, and other models). When the code P0128 is activated in some General Motors vehicles, the temperature gauge stops operating and the radiator fans operate continuously. Unless there are other concerns, replacing the thermostat is usually sufficient to resolve the problem. For the code P0128 in 2006 Chevrolet Malibu, Impala, Pontiac G6, and a few other vehicles, a 2007 General Motors Technical Service Bulletin proposes reprogramming the PCM as a remedy.

According to the Mazda service notice, the code P0128 may be caused by incorrect calibration of the PCM (engine computer) in some early Mazda 3 and Mazda 5 model year vehicles.

Subaru service bulletin 09-56-13 is available.

It was discovered that resetting the PCM (engine computer) is recommended when the code P0128 is detected in a handful of Chrysler technical service bulletins for many Jeep and Dodge models.

In this case, a shim should be used in conjunction with a thermostat housing that has been modified.

How the thermostat works

Thermostats are temperature-controlled valves that are fitted in the vehicle’s cooling system. It regulates the flow of coolant through the radiator and aids in and protects the radiator from overheating. Read more:Thermostat: how it works, what it looks like, what it causes, what it tests. Many contemporary automobiles have thermostats that are regulated electrically.

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Most auto stores sell infrared theremostats for about $20, and they may be used for a variety of purposes, including heating and cooling. Try pointing it toward the thermostat housing and recording the temperature that results. On the transaxle valve body assembly, there is an oil temperature sensor that measures the temperature of the oil. The temperature sensor with one wire is located on the thermostat housing. The single wire appears to be connected to the fan circuit and the dash gauge. As a result, the three wires must be for the CPU.

However, when two coolant temperature sensors are employed, this is the most common configuration.

As a result, you may need to perform more testing or replace the other two sensors.

In order to clear the code if it keeps appearing, disconnect the negative battery wire for 1 minute and the ECU will be reset.

What is Trouble Code P0128 – Coolant Below Thermostat Regulating Temperature

Thermostat for the coolant (Coolant Temperature Below Thermostat Regulating Temperature)

Here is what a P0128 means, in simple terms

The P0128 trouble code indicates that your engine is operating at an excessively high temperature. This sounds fantastic, doesn’t it? In actuality, it isn’t. An engine that is unable to reach the necessary temperature in the requisite amount of time may result in an increase in dangerous emissions. So the Engine Control Module (ECM) is configured to recognize low engine coolant temperature (when compared to ambient air temperature and a pre-determined value), as well the pace at which the pre-determined engine coolant temperature must be achieved.

What caused my vehicle to set a P0128 trouble code?

The Engine Coolant Temperature (ECT) sensor is used by the engine control module to assess whether or not an OBD-II P0128 code should be generated. Any time a trouble code P0128 appears by itself, a shop technician is likely to believe that the sensor for the engine coolant temperature or the thermostat is malfunctioning.

  • A coolant thermostat that is either jammed open or opens prematurely
  • Engine coolant temperature (ECT) sensor and/or ECT wire (most commonly at the ECT connection/harness) that are not functioning properly

What symptoms will my vehicle experience when trouble code P0128?

  • Your vehicle’s check engine light (CEL), Malfunction Indicator Lamp (MIL), or Service Engine Light (SEL) is illuminated when the engine is running. When the ECC detects an issue with the engine coolant temperature, a light will be lighted and freeze frame data will be saved, containing information on the engine sensor data at the moment of detection. In addition, the trouble code P0128 will be logged in the ECM ROM memory. The engine will take an excessive amount of time to warm up (particularly on cold days)
  • Because it uses the engine’s coolant to heat the vehicle’s interior, the air conditioning heater may not be able to achieve the desired temperature because the coolant never reaches its maximum working temperature. Because the correct engine operating temperature is not attained quickly enough, the smell of HC (hydrocarbon) lingers for a longer period of time than is typical during engine beginning.

How can I fix a P0128 problem and where should I start?

We recommend that you start by checking to see if your engine’s thermostat is functioning properly. A properly functioning thermostat should only let the flow of coolant after the coolant has reached the right operating temperature (usually around 200f). Start your engine (from a cold start) and observe the temperature of the radiator hose that is connected to the thermostat housing to determine whether or not the thermostat is working properly. To begin with, the hose should be chilly to the touch, but it should quickly become quite hot (after around 3-5 minutes depending on ambient air temperature).

If you do not notice a sudden increase in the hose’s exterior temperature and instead feel the hose gradually getting warmer, your vehicle may have a thermostat that is stuck open, which allows coolant to flow through the radiator immediately after the engine is started.

Providing the thermostat is performing as it should, the next component to be checked is the engine coolant temperature sensing device.

Check for reference voltage from the ECM to the ECT while the ignition is turned on and the engine is turned off.

After that, start the engine and measure the voltage across the ECT signal line.

However, because the values vary from car to vehicle, we will not go into specifics about what voltage you should be seeing here.

The most crucial thing to pay attention to is whether or not there is a voltage fluctuation.

As a final precaution, make certain that you take the reading after the ECT connection and at the ECT sensor. In this way, you may establish whether the problem is caused by a faulty connection, which might save you money by not having to replace the ECT needlessly.

  • The coolant hose attached to the thermostat housing should be checked periodically for a sudden increase in temperature. Examine the ECT signal and the reference voltage for any anomalies. Check the ECT connection for damage.

Can I drive my vehicle with a P0128 trouble code and illuminated CEL?

  • You may be able to use your car while the P0128 problem code is displayed. Except for the possibility that the temperature gauge never reaches normal levels and that the Check Engine light is lighted, you will not notice any problems with your vehicle. In addition, if your vehicle is required to undergo smog testing, the presence of the P0128 trouble code and the presence of the check engine light will result in the vehicle failing the test. The check engine light or malfunction indicator lamp is illuminated while the P0128 trouble code is recorded in the ECC.

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